subordinate clause [duplicate]

I'm looking for a grammatical explanation for this clause

Men tend to talk about fewer subjects, the most popular being work, and sport.

In other words, we could say "..., among which, work and sport are the most popular". But I can't find a grammatical explanation for the first one ".. being work and sport."

If you want to phrase it in grammatical terms "being" is a present participle that can replace the finite verb (in this case "are") of a non-restrictive relative clause. The latter is not a subordinate clause but an adjunct (that is it provides supplementary information).